Localization of Saturated Karst Aquifer with Magnetic Resonance Sounding and Resistivity Imagery

Abstract

To answer one of the main questions of hydrogeologists implementing boreholes or working on pollution questions in a karst environment--i.e., where is the ground water?--numerous tools including geophysics are used. However, the contribution of geophysics differs from one method to the other. The magnetic resonance sounding (MRS) method has the advantage of direct detection of ground water over other geophysical methods. Eight MRSs were implemented over a known karst conduit explored and mapped by speleologists to estimate the MRS ability to localize ground water. Two direct current resistivity imageries (DC-2D imagery) were also implemented to check their capability to map a known cave. We found that the MRS is a useful tool to locate ground water in karst as soon as the quantity of water is enough to be detected. The threshold quantity is a function of depth and it was estimated by forward modeling to propose a support graph to hydrogeologists. The measured MRS's signals could be used to calculate transmissivity and permeability estimators. These estimators were used to map and to draw a cross section of the case study site, which underline accurately the known karst conduit location and depth. We also found that the DC-2D imagery could underline the karst structures: It was able to detect the known cave through its associated faults. We prepared a computer simulation to check the depth of such a cave to induce resistivity anomaly which could be measured in similar conditions.

Using 2D inversion of magnetic resonance soundings to locate a water-filled karst conduit

“…The detectability of a karst conduit typically depends on its volume and its depth: for any given depth, the greater the volume of the cavity, the greater the difference between the karst MRS response and those of the surrounding environment. This contrast makes it possible to reliably identify the water-filled cavities (Vouillamoz et al, 2003). In 2003, the karst conduit was reliably detected and these preliminary results provided encouragement for a more comprehensive study at this site.…”

“…Magnetic Resonance Sounding (MRS) is one of the most recent surface geophysical methods developed for groundwater investigation and its utility in locating water-filled karst cavities has recently been demonstrated (Vouillamoz et al, 2003). In this paper we present a methodology for the acquisition and interpretation of MRS data from soundings performed above a known karst system at Poumeyssens in the Causse de Gramat (Lot Department, SW France).…”

Análise integrada de dados de sensoriamento remoto, geologia e geofísica no estudo de aqüífero fraturado, Lindóia - SP

“…As rochas cristalinas fraturadas apresentam um grande potencial para a acumulação deágua, porém para que se obtenha sucesso em perfurações de poçosé necessário que se avaliem de modo mais preciso os recursos e as ocorrências dos aqüíferos fraturados em relação aos condicionantes geológicos. Métodos geofísicos elétricos são utilizados com sucesso na caracterização de aqüíferos fraturados, com a identificação da espessura do manto de intemperismo, profundidade do topo rochoso, fraturas preenchidas porágua e conseqüentemente na determinação de locais para a perfuração de poços (Palacky & Kadekaru, 1979;Carruthers & Smith, 1992;Hazell et al, 1992, Gallas, 2000Gallas, 2003;Vouillamoz et al, 2003).…”

“…Considerando-se um mesmo tipo litológico, as fraturas preenchidas porágua apresentam um comportamento de baixa resistividade (alta condutividade) em meio a valores de alta resistividade (Gallas, 2000;Gallas, 2003;Vouillamoz et al, 2003). Segundo Gallas (2003), a interpretação prévia de fotografias aéreasé fundamental para o melhor posicionamento da malha dos ensaios geofísicos, de modo que os perfis geofísicos sejam transversais as estruturas identificadas.…”

Determining the role of lineaments in underground hydrodynamics using Landsat 7 ETM+ data, case of the Chott El Gharbi Basin (western Algeria)

“…Generally, the Geophysical methods and especially, the electric prospecting allow specifying the location and the depth of the tectonic discontinuities susceptible to be a seat of the groundwater circulation. Indeed, they allow determining with a better precision the positioning of hydrogeological interest zones (Israel et al 1996;Thomas et al 2002;Vouillamoz et al 2003;Boutaleb et al 2009;Sombo et al 2011;Kouassi et al 2014).…”